The present invention relates to a picture signal processing system and, more particularly, to a picture signal processing system suitable for reproducing continuous tone pictures.
The display or reproduction of bi-level pictures is most stable for display devices such as a thermal printer and a liquid crystal display. To display or reproduce an ordinary picture including a continuous tone picture such as a photograph by these devices, a continuous tone display system using a dithering method is well known. According to the dithering method, a threshold value for bi-level quantization is fluctuated in accordance with a random or pseudo-random function during the process of quantizing a continuous tone picture signal to two values. In the case of this dithering method, however, the reproduction resolution is reduced and irregular noises are caused when the picture is reproduced in various tones.
A color printer using a color image sensor of the spatially divided type is well known. With such a color printer when a printed document having characters and a continuous tone color picture is copied, dots forming the continuous tone color picture are outputed as noise to thereby prevent the colors of the picture from being faithfully reproduced. In order to reduce or eliminate noise, the picture may be blurred by an optical system. When it is done so, however, even the characters are blurred, thus adversely affecting the reproduction of the characters. Blurred picture can also be obtained by an electrical process of averaging picture signals, with the result that small characters cannot be displayed.